Most investigations on the nature of the vascular dysfunction in hemorrhagic shock have implied changes in microcirculatory behavior from observations of changes in peripheral vascular resistance. A few studies have yielded direct qualitative observations of the microcirculation during hemorrhage but these have required general anesthesia and exteriorized tissues. Recent work has indicated that the bat (Myotis species) is an appropriate shock model for the investigation of changes in the microcirculation without the complications of major surgery and anesthesia. This project concerns a direct quantitative investigation of the responses of small arteries and veins and precapillary sphincters to hemorrhagic hypotension. Responses will be quantitated for the subcutaneous microvasculature in the wings of unanesthetized bats (Myotis species) and for the microvasculature in the cremaster muscle of the anesthetized rat during reversible and irreversible shock states. Experiments with anesthetized bats will allow differentiation of the effects of anesthesia and comparisons between muscle and skin microvasculatures during hemorrhage. The relative significance of the effects of innervation, intravascular pressures, and blood chemistry on small artery and vein diameters and on precapillary sphincter behavior during hemorrhage will also be determined. In general, our current hypothesis focuses on the venules as a microcirculatory segment which is critically altered during irreversible hemorrhagic shock. Techniques include closed-circuit television microscopy and on-line electronic analysis of video signals to allow measurements of small artery (30-60 micra) and small vein (50-100 micra) diameters, the duration of precapillary sphincter closure, erythrocyte flux (rbc/sec) in individual capillaries, and capillary hematocrit in bats and rats. A modified Wiederhielm servo-system is used for microvascular pressure measurements.